I guess it depend of the girl. If you take Mountain Lily, she is meh before blooming. But once she got her 3rd ability with counter power, she will be one of the best event counter with +20% defense, defense x2 counter damage and ability to do super blue counter.
My counter team is made with Camelia, Poppy, Hyperloli, Mountain Lily and Echeveria.
Only Poppy is a gacha couter and only because she is 2 slot with 100% counter. Moutain Lily and Echeveria can deal over 35k damage with super effective critical super counter damage. More than most of my other girls. Camelia is here only for +20% defense boost and evade ability.
I can't really judge the true power of counter gacha girl since I got only two: Poopy and Justicia. But if Poppy can be enough good to rivalize with event girls, Justicia can't. That's why she is in my skill activation team instead of counter team.